A content delivery network or content distribution network (CDN) is a large distributed system of servers deployed in multiple facilities (e.g., data centers) across the Internet. The goal of a CDN is to serve content to end users with high availability and high performance. CDNs serve a large fraction of the Internet content today, including web objects (text, graphics and scripts), downloadable objects (media files, software, documents), applications (e-commerce, portals), live streaming media, on-demand streaming media, and social networks.
YouTube® relies on a massive and globally distributed CDN to stream the billions of videos in its catalogue. Unfortunately, there is very little or no information published about the design and internals of this CDN. This combined with the pervasiveness of YouTube® poses a big challenge for Internet Service Providers (ISPs), which are compelled to constantly optimize end-users' Quality of Experience (QoE) without having any control on the characteristics of the CDN.